The magnetic field typically produced by rare-earth magnets can be 1.4 Tesla, whereas ferrite or ceramic magnets typically exhibit fields of only 0.5 to 1 Tesla.
Classified under permanent magnets, rare-earth magnets have a permanent magnetic field. When metallic objects are in close distance, the magnet attracts them. Some important characteristics used to compare permanent magnets are remanence, which measures the strength of the magnetic field, coercivity, the material's resistance to becoming demagnetized, energy product, the density of magnetic energy, and Curie temperature – the temperature at which the material loses its magnetism. Rare-earth magnets have higher remanence, much higher coercivity and energy product, but lower Curie temperature than other types of magnets.
Types of Rare-Earth Magnets
The two types of rare-earth magnets classified according to the materials which the magnets are made of are Samarium-cobalt and Neodymium magnets.
Samarium-cobalt magnets were the first family of rare-earth magnets. These rare-earth magnets are less used than neodymium magnets because of their higher cost and weaker magnetic field strength. Samarium-cobalt rare-earth magnets are highly resistant to oxidation. Sintered samarium-cobalt rare-earth magnets are brittle and prone to chipping and cracking and are not resistant to thermal shock.
Neodymium rare-earth magnets are the strongest and most affordable type of rare-earth magnets. Neodymium alloy is made of Neodymium, Iron, and Boron. Neodymium rare-earth magnets are usually used in computer hard drives and a variety of audio speakers. Though neodymium rare-earth magnets are inferior to samarium-cobalt in resistance to oxidation and Curie temperature, they show highest magnetic field strength. Protective surface treatments can be done with gold, nickel, zinc, tin, or epoxy resin to protect against corrosion.
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Features and Applications
The most import feature of rare-earth magnets are the superior magnetic field of all natural magnets available. Also, rare-earth magnets have become less expensive and hence widely used in applications.
The main use of rare-earth magnets are in hard drives, speakers, magnetic levitation turbines, roller coasters, and computers. Rare-earth magnets are also widely used in musical instruments and baby toys.